Porous glass that is manufactured by utilizing the phenomenon of phase separation of glass is expected to find industrial applications as an optical material having a variety of optical features such as anti-reflection.
Porous glass that utilizes the phenomenon of phase separation of glass can be obtained generally by heat treatment borosilicate-based matrix glass that is found in a phase-separable composition range at 500° C. to 700° C. in order to cause the matrix glass to give rise to phase separation and subsequently turning porous by acid etching.
To obtain a porous glass material having excellent optical features such as anti-reflection, the formation of a porous glass structure importantly needs to be broadly controlled. The above-described known process provides a low degree of freedom of forming a porous structure and the obtained porous glass normally includes a single pore size so that the obtained optical performance is limited.
Techniques have been disclosed to provide glass with intended functional features by executing a specific process on glass in order to prepare porous glass having a variety of functional features.
PTL 1 discloses a porous glass coated with an organic polymer. PTL 2 discloses a method of manufacturing a composite material by applying a liquid dispersion of a nonviscous heat-resistant resin composition onto a specifically corroded glass surface and then curing the resin. PTL 3 discloses a substrate for preparing a plated circuit by applying a phase-separating ingredient onto a glass substrate containing SiO2, heat-treating the glass substrate with the phase-separating ingredient for phase separation and subsequently removing only the phase containing SiO2 to a small extent.
According to PTLs 1 and 2, a resin substance is applied onto glass having a porous structure in order to provide the glass with an environmental stability feature such as an antifouling property. PTL 3 describes the use of PYREX (registered trademark) and quartz glass that can hardly be turned porous for a glass substrate roughening SiO2 in Example. The PTL 3 teaches a method of roughening a glass surface for the purpose of improving the adhesion between glass of a substrate and a metal plating film to be formed thereon.
While techniques of providing a glass substrate with an environmental stability feature such as an antifouling property and a surface roughening feature by coating for the glass surface have been disclosed as above, no technique of broadly controlling the formation of a porous glass structure by means of phase separation are known to date.